Lubricating coatings of ethylene/vinyloxyethanol interpolymers on metal surfaces



United States Patent LUBRICATING COATINGS 0F ETHYLENE/VI- NYLOXYETHANOLINTERPOLYMERS 0N MET- AL SURFACES John D. Calfee, Des Peres, Mo.,assignor to Monsanto Company, a corporation of Delaware No Drawing.Original application Dec. 28, 1959, Ser. No. 862,089, now Patent No.3,141,908, dated July 21, 1964. Divided and this application Feb. 10,1964, Ser- 4 Claims. (Cl. 117-127) This application is a division of mycopending application Ser. No. 862,089 filed Dec. 28, 1959 which is nowPatent 3,141,908.

The present invention concerns ferrous metals coated with lubricatingfilms of ethylene/vinyloxyethanol interpolymers.

The ethylene/vinyloxyethanol interpolymers useful in the presentinvention are low molecular weight polymers and generally of kinematicviscosities in the range of about 5 centistokes to 10,000 centistokes at100 F.

The interpolymers are characterized by their low coefficient offriction, particularly coefficients less than 0.130 dynes/squarecentimeter as measured by Kyropoulos four-ball pendulum, and bygenerally having weight percent of vinyloxyethanol in the interpolymerof between about 20% and about 70%. Even more advantageous coetficientsof friction are obtained in the range of about 30% to about 60% byweight vinyloxyethanol, such as coefiicients below about 0.115 dynes/square centimeter. The optimum coeflicients of friction are found in therange of about 35% to 50% by weight vinyloxyethanol. To a conisderableextent in the low molecular Weight ranges under consideration, thecoefficient of friction is independent of molecular weight. However, itwill be desirable, nevertheless, to utilize particular ranges ofmolecular weights for various functional fluid and lasticizer uses inorder to have proper viscosities and other properties, and it will benecessary in all cases to use fairly low molecular weights.

In general, the interpolymers of the present invention will be oils andof molecular Weights from about 100 to 2000, or more specifically about200 to 1500; but interpolymers in the form of greases or soft waxes andusually in the molecular weight range of about 2000 up to about 5000 orso have some value as lubricants or functional fluids, although in morelimited applications and under conditions in which they are liquid, andare to be considered as within the present invention. The foregoingmolecular weights have reference to the number average molecular Weightscalculated from freezing point depressions; (based on determination offreezing point of dilute benzene solution in standard Beckmannapparatus). It will be realized that the physical form of theethylene/vinyloxyethanol interpolymers will vary to some extent with theproportions of the monomers, purity of the interpolymer, possiblecrystallinity effects, etc., but the physical form will vary from oilsto waxes in approximately the molecular weight ranges noted above, andthe physical form will continue to change until the polymers become ahard wax in approximately the molecular weight range from 5000 to10,000. Above molecular weights of 10,000, or more emphatically above20,000, the ethylene/vinyloxyethanol polymers are true high molecularweight polymers having the tensile strengths and other properties ofsame; the latter molecular Weight values have reference to numberaverage molecular weights as calculated from solution viscosities.

While to a certain extent the lubricity of the interpolymers of thepresent invention is independent of molecular weight, it will berecognized that for most ice functional fluid and lubricationapplications, it will be necessary for the interpolymers to be pumpableliquids under the conditions of use, and for most applications theinterpolymers must have kinematic viscosities between about 5 and 10,000centistokes at 100 F., and more often between 20 and 5,000 centistokesat 100 F. At higher temperatures, the kinematic viscosities willgenerally be lower, e.g., at from about 2 to 500 centistokes at 210 F.,although higher viscosity material can be used if use exclusively athigher temperatures is contemplated. The viscosity index of the lowmolecular weight ethylene/ vinyloxyethanol interpolymers of the presentinvention is in general approximately equivalent to that of a good gradeof solvent-refined mid-continent lube oil stock, i.e., in the range ofabout to (ASTM D 576-41). However, the viscosity index will vary to someextent with molecular weight, roportions of monomers, etc., e.g., fromabout 70 to 110.

The low molecular Weight interpolymers of the present invention areconveniently prepared by low pressure, free radical-catalyzedinterpolymerization of ethylene and vinyloxyethanol. For thisinterpolymerization, any pressures less than 10,000 p.s.i. gauge areconsidered low pressure, e.g., pressures from 1,000 or 2,000 p.s.i. upto 8,000 or so p.s.i.; pressures around 5,000 p.s.i. are consideredparticularly suitable. While the molecular weight of the interpolymersis conveniently controlled by regulation of the polymerization ressures,the desired low molecular Weight interpolymers could also be obtained byvariance of other polymerization conditions, and the novel interpolymersare considered part of the invention regardless of their method ofpreparation.

The process of preparing the low molecular weightethylene/vinyloxyethanol interpolymers is generally carried out underconditions suitable for the high pressure polymerization of ethylene,except for the use of the lower pressures as specified above. Thepolymerization is generally effected at temperatures from about 50 C. to250 C., but is preferably carried out at temperatures from about 100 C.to about 200 C. It is possible to employ higher temperatures so long asthey do not cause pyrolysis or unduly rapid reaction under the reactionconditions, and it is also possible to employ lower temperatures, evendown to room temperature or the like, although the reaction will not bevery rapid at low temperatures. Moreover, when catalysts whichdissociate in the polymerization reaction are employed, it is preferredto employ temperatures high enough to cause such dissociation.

It is known that ethylene will polymerize at elevated temperature andpressure in the absence of catalysts, particularly if the ethylenehappens to contain trace small amounts of oxygen which have a catalyticeflFect. However, in preparing the interpolymers of the presentinvention, it is preferred to employ free radical initiating catalyststo insure the preparation of high molecular weight materials inreasonable reaction times. In general, ethylene polymerizationcatalysts, including oxygen, are suitable. On a weight basis, about 10to 200 parts per million of oxygen is very suitable at 20,000 to 40,000p.s.i. ethylene. Among the preferred catalysts are the peroxidecatalysts and the azo catalysts. Among the peroxide type catalysts are,for example, ditolyl peroxide, benzoyl peroxide, diacetone peroxide,succinyl peroxide, acetyl peroxide, acetylbenzoyl peroxide,metabromobenzoyl peroxide, lauroyl peroxide, 2,2-bis-t-butylperoxybutanehydrogen peroxide, zinc peroxide, peracetic acid, alkali metalpersulfates, perborates and percarbonates, ammonium persulfate,perborate and percarbonate and, in general, all those peroxide compoundswhich are either formed by the action of hydrogen peroxide on ordinaryacids or else which give rise to hydrogen peroxide on treatment withdilute sulfuric acid. These materials are peroxy compounds as defined inWebsters International Dictionary (1935) 2nd edition, [page 3 of Patent2,396,-

920 and column 3 of Patent 3,748,170]. As examples of 7 suitable azocatalysts may be mentioned bisbenzene diazosuccinate, the inorganic acidsalts of 2,2'-diguanyl-2,2- azopropane, 2,2'-azobis(methylisobutyrate)or 2,2-az- V bis(isobutyramide). The catalyst will ordinarily be em-Exznmple 1 To a jacketed tubular reactor with the jacket maintained at180 C., ethylene and vinyloxyethanol were continuously charged in aboutequal proportions by weight along with 0.2% by weight of ditertiarybutylperoxide and polymerized at a pressure of 5,000 p.s.i. gauge. The peaktemperature in the reactor was 200 C. The conversion to copolymer wasbetter than 20%.

The interpolymer obtained by the foregoing polymerization was treatedwith a large volume of hot acetone and filtered to remove acetoneinsolubles. The acetone was then evaporated from the acetone-solubleportion of the interpolymer, which was characterized as follows:

Weight percent hydroxyl 8.23 Weight percent vinyloxyethanol 42.6Gardner-Holt viscosity (Stokes) 32 Pour point, F. 28 Specific viscosity(measurement at 25 C. on

solution in pyridine) 0.28

The coefiicient of friction was determined by a Kyropoulos pendulummodified with a 4-ball contact (A Con venient Measurement of FrictionCoefiicient, H. E.

Malincke, Lubrication Engineering, March-April, 1956). Polished steelballs were used as the contact in the test. The ethylene/vinyloxyethanolinterpolymer proved to have a very low coefiicient, 0.106 dyne/ squarecentimeter. This compares very favorably with values for well knownlubricants, e.g., 0.187 for mineral oil, 0.200 for glycerine, 0.232 forethylene glycol, and 0.143 for a commercial polyglycol syntheticlubricant. The ethylene/vinyloxyethanol interpolymer exhibited goodtemperature stability as shown by relatively slight changes in viscositywhen the interpolymer was maintained at 100150 C. for several days.

Example 2 An interpolymer was prepared which had approximately theproportions of monomers of that of Example 1,

but slightly higher molecular weight; the weight percentcentistokes at210 F., and viscosity index of 95.3 (ASTM Example 3 Ethylene andvinyloxyethanol were copolymerized in charge proportion of 1 to 3 (byweight), utilizing 1% by weight of ditertiarybutyl peroxide as catalyst.The pressure was 5,000 p.s.i., jacket temperature 165-170" C.,

and internal peak temperature about 185 C., and good conversion wasobtained.

The interpolymer was characterized as follows:

Weight percent hydroxyl 1 1.59

Weight percent vinyloxyethanol 60.1 Gardner-Holt viscosity (Stokes) 32Pour point, F. 28 Specific viscosity (measurement at 25 C.," on 5%solution in pyridine) 0.28

The coefficient of friction was 0.115 dyne/square centimeter. Kinematicviscosity was 4977.9 centistokes at F., and 129.3 centistokes at 210 F.,and viscosityindex was 98.7.

Example 4 Ethylene, 60 parts, and vinyloxyethanol, 20 parts, were 7 ininterpolymerized in the presence of 20 parts acetone, all parts being byweight. Ditertiarybutyl peroxide, 0.5%,

was employed as initiator and the polymerization conditions wereapproximately those of Example 1. I

The acetone-soluble portion of the interpolymer oil was characterized asfollows:

Weight percent hydroxyl 4.68 Weight percent vinyloxyethanol 24.3Gardner-Holt viscosity (Stokes) 5 Pour point, F. 20 Specific viscosity(measurement at 25 C. on 5% solution in pyridine) 0.195

The coefficient of friction was 0.122 dyne/square centimeter. Kinematicviscosity was 218.7 centistokes at 100 F. and 16.83 centistokes at 210F. and viscosity index was 87.7.

A low molecular weight ethylene/vinylethanol interpolymer oil having avinyloxyethanol contentof about 13% by weight had a coefficient offriction of 0.138 dyne/square centimeter, as determined by the methodemployed in the examples above.

A low molecular weight vinyloxyethanol homopolymer was determined tohave a coefiicient of friction of 0.146 dyne/ square centimeter.

Several samples of ethylene/vinyloxyethanol copolymer were tested forantiwear properties by the Shell 4- Ball WearTest (600 r.p.m., 10kilogram weight, 167 F., for one hour, 52-100 siteel-on-steel). Theethylene/ vinyloxyethanol copolymer of 42.5% vinyloxyethanol content hadvery good antiwear properties as shown by a scar diameter of only 0.27mm. This compares very favorably withvalues such as 0.41 mm. forethylene glycol, 0.48 mm. for white oil, 0.61 mm. for parafiin oil, and0.45 mm. for tn'cresyl phosphate. An ethylene/vinyloxyethanol copolymerof 60% vinyloxyethanol content had a value of 0.29 mm., and a 24.7%vinyloxyethanol content copolymer also had a value below the 0.50 mm.

value used as a criterion of antiwear properties.

While the friction tests above were made utilizing polished steel ascontact, this metal was selected as a recognized standard for testinglubricants, and the results are translatable with reasonable accuracy toother metals such as other steels, irons, ferrous metals in general,polished chromes, etc., and in general, the results indicate the valueof the interpolymers in reducing friction, particularly with respect tothe foregoing metals, but also for aluminums, brasses, bronzes, coppers,etc. 7

The low coefficients of friction of the interpolymers of the presentinvention will, of course, suggest various lubricating uses, but onlya-few of the more important uses will be listed herein. Theethylene/vinyloxyethanol interpolymers can be used to lubricate metalbearings orin any other applications involving ferrous metals coated Vwith lubricating films or in which a film of the interpolymers separatesmetal surfaces in close juxtaposition with each other, particularly whenthere is relative movement of the surfaces. The low molecular weightethylene/vinyL oxyethanol interpolymers will also be useful in variousfunctional fluid applications, i.e., as automotive hydraulic brakefluids, power transfer fluids, and the like. In many lubrication andfunctional fluid applications, the ethylene/ vinyloxyethanolinterpolymers will be used in compositions along with other materialsuseful in such applications, e.g., along with mineral oils, and in somecases it will be desirable to modify the ethylene/vinyloxyethanolstructure in various ways to improve compatability with or solubility insuch other materials. In addition, the free hydroxyl group of the lowmolecular weight ethylene/ vinyloxyethanol interpolymers provides areactive site and makes the interpolymers suitable intermediates for thepreparation of various modified polymers.

An application related to lubricating uses is the use of low molecularweight liquid or waxy ethylene/vinyloxyethanol interpolymers, or lowmolecular weight vinyloxyethanol homopolymers as leather softeners; thereferred to polymers also make leather water repellant and morereceptive to stains and polishes, and leathers impregnated with suchpolymers constitute part of the present invention. Leathers can suitablybe impregnated by brushing or rubbing the stated polymers into theleather, or by merely permitting the polymer oils to soak into theleather.

It will be realized that the molecular weight values and percentages ofmonomer values in the copolymers as described herein represent averagesand that values for some specific molecules may differ considerably fromthe average values. Fractionation of the copolymers into fractionssoluble in acetone or hexane or neither tends to narrow the molecularweight and compositional differences, and it is believed that theacetone soluble fractions generally used in the test procedures hereinhad fairly narrow molecular Weight and compositional distributions.However, the interpolymers have the desired properties regardless oftheir method of isolation, and, moreover while narrow distributions aredesirable for testing, it appears that fairly broad molecular weight andcompositional distributions can be present in the interpolymers hereinwithout adverse elfect on coefficients of friction, so long as theaverages are as described herein.

The low molecular weight ethylene/vinyloxyethanol interpolymersdescribed are exemplified herein by low molecular weightethylene/vinyloxyethanol copolymers, but it is apparent thatsubstantially equivalent properties would be obtained if small amountsof other polymerizable vinyl monomers, e.g., up to 15% by weight or morevinyl acetate, were polymerized along with the ethylene andvinyloxyethanol, and embodiments including small amounts of such othervinyl monomers are considered within the scope of the interpolymers andcopolymers of the present invention.

What is claimed is:

1. A metal bearing surface coated with a lubricating film of lowmolecular weight ethylene/vinyloxyethanol copolymer.

2. A ferrous metal coated with a lubricating film of low molecularWeight ethylene/vinyloxyethanol interpoly-- mer having a vinyloxyethanolcontent of about 20% to about by weight.

3. A ferrous metal coated with a lubricating film ofethylene/vinyloxyethanol copolymer oil which is liquid at roomtemperature and has molecular weight in the range of about 200 to 1500having a vinyloxyethanol content of about 20% to about 70% by weight.

4. A ferrous metal coated with a lubricating film ofethylene/vinyloxyethanol copolymer having vinyloxyethanol content ofabout 30% to 60% by weight, said copolymer having kinematic viscosity offrom 5 centistokes to 10,000 centistokes at F. and having lowcoefficients of friction for steel-to-steel contacts lubricated by same.

References Cited UNITED STATES PATENTS 2,529,190 11/1950 Rocchini et a1.2,748,170 5/1956 Benoit et al 25252 X ALFRED L. LEAVITT, PrimaryExaminer.

J. R. BATTEN, ]R., Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION ent No. 332L942Dated June 1967 Inventor) John D. Calfee It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 1, line 33, "conisderable" should read --considerab1e- See specpage 1, line 21.

Column 3, line 4, "Patent 3,748,170" should read -Patent 2,748,170--.

See spec page 5, line 10.

Column 4, line 17 "in interpolymerized" should read -interpo1ymerized--.

See spec page. 8, line 3.

SIGNED AND SEALED SEP 3 01969 (SEAL) Attest:

Edwue M. Fletche Ir- WILLIAM E. sum, .11 Attcatmg Officer commissionerof Patent;

1. A METAL BEARING SURFACE COATED WITH A LUBRICATING FILM OF LOWMOLECULAR WEIGHT ETHYLENE/VINYLOXYETHANOL COPOLYMER.